And yet, one of the more ironic things about SR not getting a sequel is that Warner Bros. did greenlight a sequel in October 2006:

I hate it when studios do that and then change their minds later on, but I think WB still had hopes in that Bryan Singer would deliver a more action driven sequel in fact I think he even mentioned that the sequel would be bigger.

__________________A few of the Marvel Superheroes are somewhat niche characters that aren't extremely versatile, thus they don't have a lot of longevity potential. For example, Namor is a water guy, Silver Surfer is a space guy, Dr. Strange is a magic guy, and so on.